Heating composition



United States Patent 3,160,537 HEATlllG COMPOSITIGN Thomas R. Trafton, Jr., Middle River, Md., assignor to Catalyst Research Corporation, Pittsburgh, Pa, a corporation of Pennsylvania No Drawing. Filed Oct. 12, 1961, Ser. No. 144,552 1 (Jlaim. (Cl. 149-37) This invention relates to autogenous heating compositions for use in heating elements for supplying limited amounts of heat for such diverse purposes as heating canned foodstuffs, heating water, defrosting, sterilization.

Heretofore a variety of autogenous heating devices have been proposed and used for readily portable heat sources in which a combustible chemical mixture is placed within a vented or hermetically sealed container. The combustible compositions in use generally consist of a combustible metal and an inorganic oxidizing agent, many of which react extremely rapidly and generate extremely high temperatures. For many purposes, such as heating water, the heat is generated faster than it can be transferred to the object to be heated, which results in heat waste and the possible failure of the container due to the high temperatures reached. Heretofore, it has been customary to add substantial amounts of inert diluents, such as powdered glass, mica or silica, to the combustible composition which slows and cools the reaction by acting as a heat sink and by lowering the concentration of the active ingredients. The use of an inert diluent, however, requires a larger and heavier charge to provide a given amount of heat. I

It is an object of this invention to provide a heating composition having a modified burning rate. Another object is to provide a heating composition with a modified burning rate which contains a high proportion of active ingredients. Another object is to provide a heating composition compact which is freely releasable from forming dies. Other objects will be apparent from the following description and claims.

According to this invention, a finely divided oxidizable metal, e.g., flaked or powdered, and a finely divided inorganic oxidizing agent, preferably in substantially stoichiometric proportions, are mixed together with a minor proportion of finely divided crystalline lubricant such as graphite and/or molybdenum disulfide and, if desired, a finely dividedinert diluent. The mixture is compressed to form an autogenous combustible consolidated body which is used to provide heat in the same general manner as similar compositions have been used heretofore. The new compositions containing graphite and/or molybdenum disulfide burn at a slower rate than corresponding compositions not containing them. The graphite and/ or molybdenum disulfide also function as a die lubricant, prolonging the life of dies used in the compression of the mixtures and making the consolidated body freely releasable from the dies.

The burning rate of any of the wide variety of heretofore known combustible compositions comprising a finely divided metal and an inorganic oxidizing agent may be modified by the addition of a minor amount of graphite and/ or molybdenum disulfide. Examples of suitable metals are finely divided aluminum, zinc, nickel, antimony, zirconium, iron and their alloys, as well as various intermetallic compounds such as calcium silicide. Examples of the wide variety of suitable oxidizing agents include the pcrmanganates, such as potassium permanganate; the chlorates and perchlorates, such as those of the alkali and alkaline earth metals; inorganic oxide and peroxide, such as barium peroxide, iron oxide, litharge, manganese dioxide, and others; the chromates, such as barium chroma-te; as well as sulfur and other elements that will combine exothermically with metals. When proportioned ice stoichiometrically, or with an excess of the metal, these known compositions liberate no appreciable amount of gaseous products on burning. I have found that the new compositions of this invention do liberate a slight amount of gas on burning, so that'they should be used in vented containers or in hermetically sealed containers "having sufiicient free air space to accommodate the gas generated.

The following comparison of an old autogenous combustible composition with new compositions are illustrative of this invention. Stoichiometric portions of ZOO-mesh powdered aluminum and ferric oxide having an average particle size of about 2 microns were intimately mixed. Portions of the mixture were intimately mixed with 32 5-mesh silica fiour and/or similarly finely divided crystalline lubricants in the amounts set forth in Table I.

.The various mixtures were compacted into pellets under a pressure of 4900 p.s.i. The pellets were ignited on one side and the rate of travel of the burning front was measured. The burning rates for the various compositions are set forth in Table I.

Table I Percent, Component by Weight Component Ex.2 Ex.3 Ex.4 Ex.5

Aluminum Ferric Oxide Hone 9NPN!" coon-:00

Hone N92? 0001000 KIM E N??? OOOr-WO plute Molybdenum Disulfide- Burning Rate (inches/seea rate as one containing sixteen percent inert diluent.

Even slower burning rates may be achieved by using larger amounts of crystalline lubricant or by using both a crystalline lubricant and inert diluent. By proper selection of the type and amount of crystalline lubricant and, if desired, inert diluent, the heating composition can be tailored to provide at a desired rate the amount of heat required for a specific application.

The amount of retardation of burning rate increases with increasing amounts of lubricating additive and any amount desired may be used. Generally I prefer to use between about 0.1 and 5.0% lubricating additive; amounts smaller than 0.1% retard the burning rate only slightly, and the addition of amounts beyond 5.0% do not significantly increase the efiect of the additive.

As in the prior combustible compositions, the burning rate may be adjusted slightly by varying the pressure at which the mixtures are compressed; increasing the compression pressure will decrease the burning rate, although the effect is slight in comparison to the modification of burning rate obtained by using the crystalline lubricant.

Generally mixtures are compressed under about 1000 to 10,000 p.s.i. pressure.

The new compositions are generally enclosed in a'cartridge provided with an igniting primer, in the same manner as similar previous compositions used for heating purposes. The combustible composition mixture may be compressed directly in the containing cartridge or it may be separately compressed and the consolidated body then placed in the cartridge. Ignition may be accomplished 3 by use of an ordinary cartridge primer or a fuse. Ignition of some combustible compositions may require a supplementary starter charge which is easily ignited by primer or fuse; e.g., a stoichiometric mixture of electrolytic iron and manganese dioxide. According tothe provision of the patent statutes, I have explained the principle and method of operation of my invention and have illustrated what I now consider to represent its best embodiment. However, I desire to have it understood that, Within the scope of the appended claim, the inyention may be practiced otherwise than as specifically illustrated and described.

I claim: An autogenous combustible composition consisting 4 essentially of a compacted intimate mixture of the following finely diyide'd ingredients: about 22 to 25% aluminum, about 62 to 73% ferric oxide, 0 to about 15% inert diluent, and about 0.1 to 5.0% combustion retardant selected from the group consisting of graphite, molybdenum disulfide and mixtures thereof.

References Cited in the file of this patent UNITED STATES PATENTS 1,901,313 Mann Mar. 14, 1933 2,424,937 Linzell July 29, 1947 2,716,599 Heiskell Aug. 30, 1955 2,976,136 Heiskell Mar. 21, 1961 

